The high entropy alloys (in English High entropy alloys = HEA) are alloys formed by mixing equal or relatively large proportions of (usually) five or more elements. These multi-component alloys have attracted considerable interest over the past decade for their intriguing structural, chemical and physical properties, but also for their ability to create an almost infinite number of unique combinations for alloy design.
This type of material is not yet used regularly in additive manufacturing, but recent advances reveal that selective laser melting, laser fusion deposition, electron beam fusion, and electric arc additive manufacturing could process these materials.
As part of a research led by Wen Chenassistant professor of mechanical and industrial engineering at UMass, e Ting Zhu, Professor of mechanical engineering at Georgia Tech, a team of scientists found that combining an HEA with laser powder bed fusion could create new materials with unprecedented properties.
Since the process melts and solidifies the materials very quickly compared to traditional metallurgy, ” we get a very different microstructure, far from equilibrium “ on the components created, explains Chen. This microstructure resembles a network and is composed of alternating layers called face-centered cubic nanolamellar structures (in English face-centered cubic = FCC) and cubic centered body (in English body centered cubic = BCC), incorporated into microscale eutectic colonies with random orientations. The nanostructured hierarchical HEA allows for the cooperative deformation of the two phases.
” The atomic rearrangement of this unusual microstructure results in very high strength and greater ductility, which is not common, since normally solid materials tend to be brittle says Chen. Compared to a classic metal casting, ” we have reached an almost triple strength and not only have we not lost ductility, but we have also increased it at the same time “, He adds. “For many applications a combination of strength and ductility is essential. Our results are original and exciting, for both materials science and engineering. “
” The ability to produce strong and ductile HEAs means that these 3D printed materials are more robust to withstand the applied deformations, which is important for designing lightweight structures to improve mechanical efficiency and energy savings. “, To explain Jie RenChen’s doctoral student and first author of the article.
The team developed dual-phase crystalline plasticity computational models to understand the mechanistic roles played by FCC and BCC nanolamelles and how they work together to give the material greater strength and ductility.
” Our simulation results show the surprisingly high strength and hardening responses of BCC nanolamels, which are essential to achieve the outstanding synergy between strength and ductility of our alloy. This mechanistic understanding provides an important foundation to guide the future development of 3D printed HEAs with outstanding mechanical properties. says Zhu.
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